The present invention relates generally to electro-optical systems, and more particularly, to a system that provides line-of-sight (LOS) alignment and stabilization of off-gimbal electro-optical passive and active sensors.
The assignee of the present invention manufactures electro-optical systems, such as forward looking electro-optical systems, for example, that include electro-optical passive and active sensors. A typical electro-optical system includes subsystems that are located on a gimbal while other subsystems that are located off of the gimbal.
In certain previously developed electro-optical systems, sensor and laser subsystems are located off-gimbal, and there was no auto-alignment of the sensor and laser lines of sight. Furthermore, there was no compensation for motion due to vibration, thermal or g force angular deformation in and between the optical paths for the sensor and laser subsystems. Large errors between the sensor line of sight and the laser line of sight were present that limited effective laser designation ranges, weapon delivery accuracy, and target geo-location capability, all of which require precise laser and sensor line-of-sight alignment and stabilization.
The resolution and stabilization requirements for third generation tactical airborne infrared (IR) systems are in the same order of magnitude as required by space and strategic systems but with platform dynamics and aerodynamic disturbances orders of magnitude higher, even above those encountered by tactical surface systems. The environments of third generation airborne system approach both extremes and can change rapidly during a single mission. However, conformance to the physical dimensions of existing fielded system is still the driving constraint.
Ideally, a high resolution imaging and laser designation system in a highly dynamic disturbance environment would have, at least, a four gimbal set, with two outer coarse gimbals attenuating most of the platform and aerodynamic loads and the two inner most gimbals providing the fine stabilization required, with the inertial measurement unit (IMU) and IR and visible imaging sensors and laser located on the inner most inertially stabilized gimbal.
In order to reduce gimbal size, weight, and cost, the assignee of the present invention has developed a pseudo inner gimbal set for use on HNVS, AESOP, V-22 tactical airborne and Tier 11 Plus airborne surveillance systems using miniature two-axis mirrors, mounted on the inner gimbal together with both the IMU and IR sensor, in a residual inertial position error feedforward scheme, to replace the two innermost fine gimbals, while maintaining equivalent performance. With increasing aperture size and constrained by maintaining the size of existing fielded systems, some tactical airborne IR systems are forced to locate the IR and visible sensors and laser off of the gimbals using an optical relay path, such as in the Advanced Targeting FLIR (ATFLIR) system.
In order to re-establish an ideal configuration, a pseudo on-gimbal IR sensor and laser configuration must be implemented, such as by using the principles of the present invention, with an active auto-alignment scheme with the use of miniature two-axes mirror technology. An active auto-alignment mirror configuration is in effect equivalent to having the IR sensors and auxiliary components, such as the laser, mounted on the stabilized gimbal.
An Airborne Electro-Optical Special Operations Payload (AESOP) system developed by the assignee of the present invention uses a hot optical reference source mechanically aligned to a laser. During calibration, the reference source is optically relayed through the laser window into the IR sensor window and steered to the center of the IR field of view with a two-axis steering mirror in the laser optical path. This mirror is also used in the operational mode to stabilize the laser beam. An additional mirror in the IR optical path is used to stabilize the IR beam. Since the alignment is performed initially during calibration and not continuously, during laser firing in the operational mode, the laser optical bench thermally drifts from the IR sensor optical bench and the two lines of sight are no longer coincident as when initially aligned. Further line-of-sight misalignments can be incurred by structural vibrational motion in and between the optical paths.
It would therefore be desirable to have a system for providing line-of-sight alignment and stabilization of off-gimbal electro-optical passive and active sensors. Accordingly, it is an objective of the present invention to provide for a system that provides for line-of-sight alignment and stabilization of off-gimbal electro-optical passive and active sensors.